In certain cases, it is necessary to carry out maintenance work in regions of industrial plants which are not accessible to operators, particularly on account of the cramped size of the maintenance region and/or on account of there being an inhospitable environment in the maintenance region. This is the case, for example, of a plant comprising regions at high temperatures, at low pressure, or alternatively at high pressure or alternatively regions which are contaminated by radioactive substances or filled with a liquid or a gas which may be harmful.
In particular, in the case of nuclear reactor plants, certain maintenance operations have to be carried out in regions which are both cramped and contaminated.
For example, in the case of pressurized water nuclear reactors, maintenance operations have to be carried out in parts of the reactor which are in contact with the primary fluid of the reactor while it is operating. Such parts of the reactor are generally highly contaminated and somewhat inaccessible, within the primary circuit, or alternatively within the reactor cavity, during maintenance operations for inspection and repair.
For example, when the nuclear reactor is shut down, inspection and repair operations are generally performed on the pressurized water reactor internals, the upper internals arranged above the core being set down in the reactor cavity to give access to the upper part of the core. The nuclear reactor upper internals are set down on a stand in the bottom of the reactor cavity, the horizontal underside of the internals being a small distance above the bottom of the cavity. Certain maintenance operations, for example for repair or inspection, need to involve means which are brought in under the surface of the internals, in a maintenance region which may be distant from the peripheral part of the lower internals. In this case, use is generally made of a remote-controlled carriage which is reserved for certain specific tasks under the upper internals.
In the case of maintenance work on the primary circuit itself, for example in the case of an operation replacing a section of primary pipe, such a method being the subject of a patent application filed on the same day as this application, it may be necessary to have a means of performing maintenance work inside a primary pipe which is accessible only from an introductory region consisting of an internal part of a component such as a primary pump or the nuclear reactor vessel. Such maintenance work inside a primary pipe of the nuclear reactor may prove necessary in order to grind down the internal part of a weld connecting a replacement section of primary pipe or to carry out various checks on the internal part of the weld.
In the case of nuclear reactors of a different type from pressurized water reactors and, in particular, in the case of nuclear reactors of the graphite-gas variety, it may be necessary, in the case of operations for dismantling these reactors, to operate in a region of short height between the set of guide tubes and the core of the nuclear reactor.
Hitherto there have been no known means for carrying out remote-controlled maintenance work in a cramped region which can be suited to various uses and which can carry out complex operations.
Maintenance devices used to carry out specific operations inside pipes are known. Such devices are used only inside pipes of a well-defined diameter or of a diameter varying within a narrow range around a mean value and for special purpose maintenance operations for which the tool was designed.
Also known, from patent FR-2 780 907 by the company FRAMATOME, is a remote-controlled multipurpose maintenance method and device for carrying out maintenance on an industrial plant such as a nuclear reactor. Such an installation comprises a robot arm of standard type comprising a supporting part and moving parts which can move with respect to the supporting part allowing movements in very varied paths, for example to pick up successive tools from a tool holder and the use of these tools in a maintenance operation of complex type, for example a dye-penetration inspection of a bimetallic weld between two nuclear reactor pipes. The robot is preferably a robot arm of anthropomorphic type having, for example, five or six axes for the motorized rotational movement of articulated elements of the robot. The robot may be fixed to the pipes that are to be inspected, using a clamping collar.
Such a method and such a device are not suited to maintenance operations in a region between two walls which are separated by a short distance or inside a pipe of any arbitrary diameter.